(A) Field of the Invention:
The present invention relates to a semiconductor device having a Schottky junction, and a method of manufacturing the same. More particularly, it relates to a semiconductor device wherein a material of higher Schottky barrier is formed on a material of lower Schottky barrier as a heterojunction, the boundary dislocations of which are passivated to reduce a leakage current, and also to a method of manufacturing the semiconductor device.
(B) Description of the Prior Art: In.sub.x Ga.sub.1-x As.sub.y P.sub.1-y mixed crystals which are lattice-matched to InP substrates, especially (InGa)As ternary mixed crystlls, exhibit as high mobilities as 8000 cm.sup.2 /V-sec at the room temperature and are expected as materials for high-speed FET's. In this regard, since a favorable Schottky junction cannot be formed, a method has been employed wherein lattice-matched (InAl)As is grown on the surface of the mixed crystal so as to form a Schottkyjunction on the grown layer (refer to FIG. 2, and H. Ohno et al: IEEE, Electron Device Lett. Vol. EDL-1, p. 154, 1980).
The material InAlAs, however, has the two disadvantages that it is very prone to oxidation because the mol ratio of AlAs is 0.5, and that it exhibits a Schottky barrier of 0.6 V which is not very high.
On the other hand, there has recently been experimentally fabricated an FET as shown in FIG. 3 wherein a thin film of GaAs having a lattice constant greatly different from that of an InP substrate is grown on InGaAs. In this case, however, a thick film of or above approximately 400 .ANG. cannot afford a good surface because of a lattice mismatching which is as great as 4%. Moreover, since dislocation networks at a very high density are existent at the boundary, the leakage current flows through the dislocations, and characteristics satisfactory for the gate electrode of an FET have not been obtained (refer to C. Y. Chen at al: Appl. Phys. Lett., Vol. 46 (1985), p. 1145, and C. Y. Chen et al: IEEE, Electron Device Lett., Vol. EDL-6 (1985), p. 20).
The stabilities of devices and the enhanced characteristics thereof are not considered in the prior arts, either.